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// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <stdint.h>
#include <memory>
#include "base/macros.h"
#include "base/memory/ptr_util.h"
#include "mojo/edk/system/dispatcher.h"
#include "mojo/edk/system/ports_message.h"
#include "mojo/edk/system/system_impl_export.h"
namespace mojo {
namespace edk {
// MessageForTransit holds onto a PortsMessage which may be sent via
// |MojoWriteMessage()| or which may have been received on a pipe endpoint.
// Instances of this class are exposed to Mojo system API consumers via the
// opaque pointers used with |MojoCreateMessage()|, |MojoDestroyMessage()|,
// |MojoWriteMessageNew()|, and |MojoReadMessageNew()|.
class MOJO_SYSTEM_IMPL_EXPORT MessageForTransit {
#pragma pack(push, 1)
// Header attached to every message.
struct MessageHeader {
// The number of serialized dispatchers included in this header.
uint32_t num_dispatchers;
// Total size of the header, including serialized dispatcher data.
uint32_t header_size;
// Header for each dispatcher in a message, immediately following the message
// header.
struct DispatcherHeader {
// The type of the dispatcher, correpsonding to the Dispatcher::Type enum.
int32_t type;
// The size of the serialized dispatcher, not including this header.
uint32_t num_bytes;
// The number of ports needed to deserialize this dispatcher.
uint32_t num_ports;
// The number of platform handles needed to deserialize this dispatcher.
uint32_t num_platform_handles;
#pragma pack(pop)
// A static constructor for building outbound messages.
static MojoResult Create(
std::unique_ptr<MessageForTransit>* message,
uint32_t num_bytes,
const Dispatcher::DispatcherInTransit* dispatchers,
uint32_t num_dispatchers);
// A static constructor for wrapping inbound messages.
static std::unique_ptr<MessageForTransit> WrapPortsMessage(
std::unique_ptr<PortsMessage> message) {
return base::WrapUnique(new MessageForTransit(std::move(message)));
const void* bytes() const {
return static_cast<const void*>(
static_cast<const char*>(message_->payload_bytes()) +
void* mutable_bytes() {
return static_cast<void*>(
static_cast<char*>(message_->mutable_payload_bytes()) +
size_t num_bytes() const {
size_t header_size = header()->header_size;
DCHECK_GE(message_->num_payload_bytes(), header_size);
return message_->num_payload_bytes() - header_size;
size_t num_handles() const { return header()->num_dispatchers; }
const PortsMessage& ports_message() const { return *message_; }
std::unique_ptr<PortsMessage> TakePortsMessage() {
return std::move(message_);
explicit MessageForTransit(std::unique_ptr<PortsMessage> message);
const MessageForTransit::MessageHeader* header() const {
return static_cast<const MessageForTransit::MessageHeader*>(
std::unique_ptr<PortsMessage> message_;
} // namespace edk
} // namespace mojo